1. Field of the Invention
This invention relates generally to rubber recycling processes, and more particularly to a rubber recycling process utilizing a chemical plasticizer and binding agent which is blended with scrap rubber, such as automobile tires, to produce an active filler composition which can be further compounded with other materials to form a composite material for combining with still other materials in the treatment, recycling, and manufacture of rubber and plastic articles.
2. Brief Description of the Prior Art
The slow biodegradable nature and increasing quantities of cured rubber articles, such as rubber tires, and cured plastic articles, such as polyethylene, polyvinylchloride, and other non-biodegradable articles, has caused worldwide concern for the environment, and many companies are making efforts to recycle these types of products. Current attempts to reclaim and re-use these articles in commercial ventures range from burning finely ground rubber, revulcanizing ground rubber, and reprocessing polyethylene. The success of these ventures depends upon the cost to render the materials reusable.
Various processes have been used for recycling waste tires into other forms for commercially use as an additive or filler for use in such things as asphalt and road paving materials. Large volumes of tall oil have been tried as a glue for ground scrap articles. Kahl Corporation has used a proprietary tall oil blend on ground tire waste as a part of a vulcanized package. Small amounts of scrap rubber may be added to virgin rubber as a filler in tire manufacturing. However, it is not cost effective since large amounts cannot be used because the curing process does not take place on a molecular level and the finished product cannot meet the new tire standards. Virgin cured rubber is usually priced lower than reclaimed rubber and has better physical properties in compounding.
Discarded tires are still not widely used in industry in molding rubber articles because of the cost of treating the scrap materials to make them acceptable for use. Similarly, there are problems associated in recycling of plastic articles such as polyethylene and polyvinlychloride (PVC) and other plastic materials. For example, the molecular weight mixing range of polyethylene has caused problems with homogeneity and performance of the finished product and, in the case of PVC, there is an environmental stigma associated with vinyl chloride.
There are several patents which disclose various processes and methods for reclaiming rubber waste.
Terhune, U.S. Pat. No. 1,450,462 discloses a method for reclaiming rubber waste which includes tearing up the waste to expose the fiber and permitting the fiber to absorb sulfuric acid.
Cude, U.S. Pat. No. 1,680,862 discloses a method for treating rubber which includes comminuting the rubber and treating it to organic acid capable of forming a water soluble soap.
Green, U.S. Pat. No. 2,879,245 discloses a tire scrap treatment method which includes reacting a rubbery polymer with a material selected from a group which includes carboxylic acids and esters of carboxylic acids.
Bunk et al, U.S. Pat. Nos. 3,652,467 and 3,681,267 disclose an adhesive composition comprising reclaim rubber and a rosin pot residue which includes dimeric monobasic acids and rosin.
Allen et al, U.S. Pat. No. 3,801,421 discloses an athletic surfacing laminate which includes a layer comprising particulate vulcanized rubber bonded with a resin.
Lee et al, U.S. Pat. No. 4,049,588 discloses a method for treating vulcanized rubber which includes contacting the vulcanized rubber with a fatty acid.
Frankland, U.S. Pat. No. 4,244,841 discloses a method for recycling rubber scrap which includes admixing the rubber with a cure mix which includes zinc stearate.
Many rubber recycling processes abrasively grind up waste rubber to form small particles. Abrasively ground rubber particles are generally flat with an irregular surface.
Other rubber recycling processes use waste rubber "buffings" which are powder-like particles produced during tire recapping operations. The rubber is skired from the tire in string-like configurations and is ground up to produce small particles. The rubber "buffings" or tire "buffings" usually do not contain steel belt or cord material from the tire. Emery buffings, or "buff rubber" has been the most widely used type of particle because of its string-like structure and low to nonexistent level of cord and steel belt materials. Untreated emery buffings are relatively soft and tend to bond better than particles produced by other methods.
The articles produced from ground rubber or buff rubber are relatively expensive due to the cost of grinding and further processing of the scrap rubber.
Some processes utilize cryogenically produced rubber particles in which the rubber is cooled in liquid nitrogen and then pulverized. The cryogenically produced rubber particles, or "cryo" rubber particles, are angular, have low surface area, and are shaped much like a jagged rock. Cryogenically produced rubber particles can be produced somewhat more economically than particles produced by other methods at ambient temperatures, but the cryo rubber particles are harder, have more abrasive resistance, and poor bonding strength. Thus, cryogenically produced rubber particles have had limited use in recycling processes.
It would therefore be desirable to utilize scrap rubber, such as automobile tires, as a main or primary ingredient in a chemical composition which can be used as an active filler in the treatment, recycling, and manufacture of rubber and plastic articles. It would also be desirable to provide a chemical plasticizer and binding agent which will plasticize, swell, and soften scrap rubber including cryogenically produced rubber.